Wax. One of the guys here had a tiny prototype camera body made on a 3-d wax printer. This was then turned into metal by investment casting. The printer was capable of producing 12um features
You would need a heater, hollow needle, some kind of pump/valve thingy, and investment casting wax, which could be just polyethylene dissolved in paraffin candle wax.

Theres also EDM, which would let you make things from very hard metals. EDM circuits can be DIY'd.